﻿Shader "UI/UIImageOutline"
{
	Properties
	{
		_MainTex ("Sprite Texture", 2D) = "white" {}
		_Color("Tint",Color) = (1,1,1,1)
		_StencilComp("Stencil Comparison",Float) = 8
		_Stencil("Stencil ID",Float) = 0
		_StencilOp("Stencil Operation",Float) = 0

		_StencilWriteMask("Stencil Write Mask",Float) = 255
		_StencilReadMask("Stencil Read Mask",Float) = 255

		_ColorMask("Color Mask",Float) = 15

		[Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip ("Use Alpha Clip",Float) = 0

		_OutlineColor("Outline Color",Color) = (1,1,1,1)
		_OutlineWidth("Outline Width",Float) = 2
		_Threshold("Threshold",Range(0,1)) = 0.5
	}
	SubShader
	{
		Tags{
			"Queue" = "Transparent"
			"IgnoreProjector" = "True"
			"RenderType" = "Transparent"
			"PreviewType" = "Plane"
			"CanUseSpriteAltas" = "True"
		}
		Stencil{
			Ref [_Stencil]
			Comp [_StencilComp]
			Pass [_StencilOp]
			ReadMask [_StencilReadMask]
			WriteMask [_StencilWriteMask]
		}
		// No culling or depth
		Cull Off
		Lighting Off
		ZWrite Off 
		ZTest [unity_GUIZTestMode]
		Blend SrcAlpha OneMinusSrcAlpha
		ColorMask [_ColorMask] 

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			
			#include "UnityCG.cginc"
			#include "UnityUI.cginc"

            #pragma multi_compile __ UNITY_UI_ALPHACLIP

			struct appdata_t
			{
				float4 vertex : POSITION;
				float4 color  : COLOR;
				float2 texcoord:TEXCOORD0;
			};

			struct v2f
			{
				float4 vertex : SV_POSITION;
				float4 color  : COLOR;
				half2 texcoord:TEXCOORD0;
				float4 worldPostion:TEXCOORD1;
			};

			fixed4 _Color;
			fixed4 _TextureSampleAdd;
			fixed4 _ClipRect;

			v2f vert (appdata_t IN)
			{
				v2f OUT;
				OUT.worldPostion = IN.vertex;
				OUT.vertex = UnityObjectToClipPos(OUT.worldPostion);
				OUT.texcoord = IN.texcoord;
				#ifdef UNITY_HALF_TEXEL_OFFSET
				OUT.vertex.xy += (_ScreenParams.zw - 1.0)*float2(-1,1);
				#endif
				OUT.color = IN.color * _Color;
				return OUT;
			}
			

			sampler2D _MainTex;
			float4 _MainTex_TexelSize;
			float4 _OutlineColor;
			float _OutlineWidth;
			float _Threshold;

			fixed4 frag (v2f IN) : SV_Target
			{
				half4 color = (tex2D(_MainTex,IN.texcoord) + _TextureSampleAdd)*IN.color;
				color.a *= UnityGet2DClipping(IN.worldPostion.xy,_ClipRect);
				#ifdef UNITY_UI_ALPHACLIP
				clip(color.a-0.001);
				#endif

				float width = _MainTex_TexelSize.z,height = _MainTex_TexelSize.w;
				if (color.a <= _Threshold )
				{
					half2 dir[8] = {{0,1},{1,1},{1,0},{1,-1},{0,-1},{-1,-1},{-1,0},{-1,-1}};

					for (int i = 0; i < 8; ++i)
					{
						float offset = float2(dir[i].x/width,dir[i].y/height);
						offset *= _OutlineWidth;

						half4 nearby = (tex2D(_MainTex, IN.texcoord+offset) + _TextureSampleAdd) * IN.color;
						if (nearby.a > _Threshold)
						{
							color = _OutlineColor;
							break;
						}
					}


				}
				return color;
			}
			ENDCG
		}
	}
}
